• Neil Horman's avatar
    [SCSI] cxgb3i: convert cdev->l2opt to use rcu to prevent NULL dereference · e48f129c
    Neil Horman authored
    This oops was reported recently:
    d:mon> e
    cpu 0xd: Vector: 300 (Data Access) at [c0000000fd4c7120]
        pc: d00000000076f194: .t3_l2t_get+0x44/0x524 [cxgb3]
        lr: d000000000b02108: .init_act_open+0x150/0x3d4 [cxgb3i]
        sp: c0000000fd4c73a0
       msr: 8000000000009032
       dar: 0
     dsisr: 40000000
      current = 0xc0000000fd640d40
      paca    = 0xc00000000054ff80
        pid   = 5085, comm = iscsid
    d:mon> t
    [c0000000fd4c7450] d000000000b02108 .init_act_open+0x150/0x3d4 [cxgb3i]
    [c0000000fd4c7500] d000000000e45378 .cxgbi_ep_connect+0x784/0x8e8 [libcxgbi]
    [c0000000fd4c7650] d000000000db33f0 .iscsi_if_rx+0x71c/0xb18
    [scsi_transport_iscsi2]
    [c0000000fd4c7740] c000000000370c9c .netlink_data_ready+0x40/0xa4
    [c0000000fd4c77c0] c00000000036f010 .netlink_sendskb+0x4c/0x9c
    [c0000000fd4c7850] c000000000370c18 .netlink_sendmsg+0x358/0x39c
    [c0000000fd4c7950] c00000000033be24 .sock_sendmsg+0x114/0x1b8
    [c0000000fd4c7b50] c00000000033d208 .sys_sendmsg+0x218/0x2ac
    [c0000000fd4c7d70] c00000000033f55c .sys_socketcall+0x228/0x27c
    [c0000000fd4c7e30] c0000000000086a4 syscall_exit+0x0/0x40
    --- Exception: c01 (System Call) at 00000080da560cfc
    
    The root cause was an EEH error, which sent us down the offload_close path in
    the cxgb3 driver, which in turn sets cdev->l2opt to NULL, without regard for
    upper layer driver (like the cxgbi drivers) which might have execution contexts
    in the middle of its use. The result is the oops above, when t3_l2t_get attempts
    to dereference L2DATA(cdev)->nentries in arp_hash right after the EEH error handler sets it to NULL.
    
    The fix is to prevent the setting of the NULL pointer until after there are no
    further users of it.  The t3cdev->l2opt pointer is now converted to be an rcu
    pointer and the L2DATA macro is now called under the protection of the
    rcu_read_lock().  When the EEH error path:
    t3_adapter_error->offload_close->cxgb3_offload_deactivate
    Is exectured, setting of that l2opt pointer to NULL, is now gated on an rcu
    quiescence point, preventing, allowing L2DATA callers to safely check for a NULL
    pointer without concern that the underlying data will be freeded before the
    pointer is dereferenced.
    
    This has been tested by the reporter and shown to fix the reproted oops
    
    [nhorman: fix up unitinialised variable reported by Dan Carpenter]
    Signed-off-by: default avatarNeil Horman <nhorman@tuxdriver.com>
    Reviewed-by: default avatarKaren Xie <kxie@chelsio.com>
    Cc: stable@kernel.org
    Signed-off-by: default avatarJames Bottomley <JBottomley@Parallels.com>
    e48f129c
cxgb3_offload.c 37.1 KB